In recent years there has been greater demand for mechanical seal constructions which are of the double or tandem type so as to permit continued operation of an apparatus even if one of the seals should fail. With this type of construction, the stationary seal ring normally has a rotatable seal ring urged into sliding sealing engagement with each axial end thereof. The two rotatable seal rings, as disposed on opposite sides of the stationary seal ring, are often referred to as the inner and outer seals. With this double seal arrangement, an intermediate chamber is formed within the seal construction between the two seals in surrounding relationship to the shaft, and a buffer or cooling fluid is supplied to this chamber so as to cool the seal faces. The buffer fluid is circulated through a closed system by an auxiliary pump disposed externally of the seal construction. With this arrangement, the two seals operate in tandem when the buffer fluid is at a very low pressure so that the inner seal forms the primary seal, but if the high pressure working fluid leaks into the buffer chamber, then the outer seal prevents leakage. Alternately, a high pressure buffer fluid can be supplied to the buffer chamber, which buffer fluid is at a pressure higher than that of the working fluid, whereby the arrangement then functions as a double seal for preventing leakage of the working fluid.
While several manufacturers have attempted to utilize seals of this latter type over the past several years, nevertheless one of the common drawbacks of this double or tandem seal arrangement is the excessive heat generated thereby, and hence the difficulty of circulating adequate quantities of coolant or buffer fluid through the seal construction. The necessary circulation has been achievable solely by means of an auxiliary pump disposed externally of the seal construction, although most users have objected to such a system since the necessity of having to utilize an auxiliary pump for the cooling or buffer fluid necessarily increases the complexity and hence unreliability of the system. For this reason, the known double or tandem seal constructions have achieved only marginal acceptance and success.
In recognition of this problem, namely the adequate circulation of buffer or cooling fluid, one manufacturer has attempted to incorporate a pump within the mechanical seal construction. This has been accomplished by fixedly and concentrically securing an elongated pumping sleeve within the seal stator in surrounding relationship to the rotatable shaft. This pumping sleeve has a spiral pumping groove formed in the inner peripheral surface thereof. With this arrangement, however, the spiral pumping groove and its small cross section creates a severe restriction on the quantity of fluid which can be pumped or recirculated, and hence the effectiveness of this arrangement is seriously questionable. Further, this pumping sleeve occupies substantial space both axially and radially, whereby the overall seal construction becomes of greater size, and hence will not always fit within the stuffing box on some types of equipment.
Accordingly, the present invention relates to an improved mechanical seal construction which overcomes the above disadvantages. More specifically, the improved mechanical seal construction of this invention can be utilized as either a double or tanden seal, and incorporates as an integral part thereof a pumping structure which is intimately associated with the interior chamber for the buffer fluid so as to effect efficient circulation of substantial quantities of buffer fluid to thereby effect optimum cooling of the seal construction, whereby use of an auxiliary pump is hence obviated. Further, this improved mechanical seal construction, and specifically the pumping structure which is intimately and integrally associated therewith, is extremely small and compact, and in fact is formed directly on the seal stator and the shaft sleeve, whereby additional components or elements are not required for incorporation within the seal construction, thereby enabling the seal construction to maintain minimum axial and radial dimensions.
In this improved seal construction, the shaft sleeve is provided with surface irregularities thereon, such as a series of circumferentially spaced slots, so that the shaft sleeve functions as a pumping rotor. The surrounding seal stator, namely the gland insert, has supply and discharge ports extending radially therethrough, which ports extend substantially tangentially with respect to the shaft sleeve so that the latter, due to its rotation, will effectively pump and hence circulate the cooling or buffer fluid through the buffer chamber and through the external circuitry for the fluid.
This improved seal construction additionally is of a balanced construction, that is, the axial forces imposed on the rotating seal rings by the working fluid and hence transmitted onto the seal faces, are imposed over an area which is slightly less than the area of engagement between the seal faces so as to minimize heat generation on the seal faces. The seal construction also preferably utilizes a single large-diameter coil spring in surrounding relationship to the shaft sleeve for urging the seal ring against the stator, thereby minimizing the possibility of hang-up and providing the construction with added corrosion resistance, particularly when used as a tandem arrangment.
In addition, this improved seal construction, and particularly the provision of the integral pumping structure associated therewith, enables the seal construction to be utilized with higher pressures and higher speeds, while at the same time eliminating costly auxiliary pumping equipment.
Other objects and purposes of the invention will be apparent to persons familiar with seal constructions of this general type upon reading the following specification and inspecting the accompanying drawings.